In recent years, as a nuclear medicine imaging apparatus, a positron emission computed tomography apparatus (hereinafter, referred to as a PET apparatus) has been known. The PET apparatus generates, for example, the functional image of body tissues. Specifically, in the imaging operation of the PET apparatus, first, a medicine including positron emitting nuclides is given to the subject. Then, the positron emitting nuclides that are selectively introduced into the body tissues of the subject emit positrons and the emitted positrons are coupled to electrons and are then extinguished. In this case, the positron emits a pair of gamma rays substantially in the opposite direction. The PET apparatus detects the gamma rays using detectors that are arrange in a ring shape around the subject and generates a coincidence list from the detection result. Then, the PET apparatus performs reconstruction using a back projection process on the basis of the generated coincidence list, thereby generating a PET image.
In recent years, a PET apparatus having a time of flight (TOF) function has appeared. A PET apparatus that does not have the TOF function performs reconstruction on the assumption that the positrons are present with equal probability on a line of response (LOR) linking a set of detectors that detect a pair of gamma rays. In contrast, the PET apparatus having the TOF function calculates the spatial position of the positron on the LOR using the difference between the detection times when the set of detectors detect the gamma rays. The PET apparatus having the TOF function adds the calculated spatial position and performs reconstruction using the back projection process, thereby generating a PET image.
However, in the related art, it takes a long time to reconstruct an image using the back projection process. As a result, it takes a long time to generate a PET image. For example, in the related art, it takes a few minutes to generate the PET image after the image operation is performed by the PET apparatus. Therefore, it is necessary to reduce the time required to generate the PET image.